Flexible wing-sail and wind-propelled vehicle including same

ABSTRACT

A flexible wing-sail for wind-propelled vehicles includes a mast to be rotatably mounted in a vertical position on the vehicle, a plurality of flexible sail panels carried by the mast, and a spreader assembly secured to battens in the sail panels for securing them to the mast and for imparting to them an airfoil shape having a leading edge fore of the mast, and a trailing edge aft of the mast. The spreader assembly includes a fixed spreader unit secured to the sail panels at the bottom of the wing-sail and fixing it to the bottom of the mast, and a plurality of slidable spreader units secured to the sail panels at longitudinally spaced locations and slidable along the mast to permit hoisting and reefing the wing-sail. The wing-sail further includes a boom pivotally coupled to the bottom of the mast and having a sliding coupling with respect to the sail panels at the trailing edge of the wing-sail, and a brake for selectively locking the mast against rotation, such that pivoting the boom while the mast is locked, changes the curvature of the airfoil shape defined by the sail panels.

This application claims the benefit of Provisional Application No.60/274,222, filed Mar. 9, 2001.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to flexible wing-sails and towind-propelled vehicles including flexible wing-sails. The invention isespecially useful in wind-propelled water vehicles, and is thereforedescribed below with respect to such application, but it will beappreciated that the invention could also be used in other applications,such as for propelling vehicles over land or ice.

The conventional water vehicle sail functions in most wind directionslike a wing of lower aerodynamic efficiency than an aircraft wingbecause the sail is a single sheet of fabric and also because the sailform is dictated by the vehicle structure. The conventional sailincludes a fixed mast, fixed points at which the sail is anchored to thevehicle, and a single-surface structure. These features do not enablesuch a sail to have high aerodynamic efficiency, but rather result inits having a lower lift/drag ratio than that of an aircraft wing.

In recent years, a number of wing-sails have been proposed for use inwater vehicles in order to better exploit the wind forces for propellingthe vehicle. Basically, a wing-sail includes two curved surfacesdefining a wing which is relatively thick and rounded at its leadingedge, and tapers in thickness to its trailing edge. When the rounded,leading edge of an asymmetrical wing-sail is oriented to face the wind,the difference in air pressure between its two curved surfaces creates alifting force which, in the case of wind-driven vehicles, is translatedto a forward propulsion force. Examples of various constructions ofwing-sails heretofore proposed are described in U.S. Pat. Nos.4,685,410; 4,733,624; 4,856,449; 4,895,091; 5,406,902; 5,575,233;5,622,131; and 6,141,809, and in U.K. Patents 2,008,514; and 2,196,310.

However, the proposed solutions to the problem generally were partialonly. They included the option of a rotating mast that carries with itthe usual rigging and sails as well as a rigid wing that cannot bereefed. Where a soft wing-sail was proposed permitting reefing, thewing-sail had an airfoil shape which is symmetric, wholly or partly andtherefore was not sufficiently efficient. Several suggested solutionsproposed an asymmetric airfoil, but the departures from symmetry arelimited to a movable surface in the rear part of the wing-sail. Othersolutions that were suggested are limited in flexibility, or are socomplex that it is doubtful whether they could function under marineconditions. In most suggested solutions, the asymmetric variations arelimited to two positions only (port/starboard), without control of thecurvature of the airfoil shape of the wing-sail.

There is therefore a definite need for a flexible wing-sail constructionproviding increased aerodynamic efficiency, capable of being reefed andtaken down, of being pointed to the wind, of enabling changes of theairfoil shape to either port or starboard in accordance with theapparent wind direction, and of enabling changes in the rate ofasymmetry of the airfoil shape in accordance with the apparentwindforce. Such higher efficiency would enable the attainment of higherspeeds of travel, or alternatively, a reduction in the size of thesails, rigging and keel. It would also enable sailing a vessel moreclosely to the wind, less heeling, and more convenience in operatingwind-driven vehicles, not only water vehicles, but also land and icevehicles.

OBJECTS AND BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a flexible wing-sailfor a wind-propelled vehicle having a number of advantages in the aboverespects as will be described more particularly below.

According to one aspect of the present invention, there is provided aflexible wing-sail for wind-propelled vehicles, comprising: a mast to berotatably mounted in a vertical position on the vehicle;

a plurality of continuous flexible sail panels carried by the mast; anda spreader assembly securing the flexible sail panels to the mast andimparting to the flexible sail panels an airfoil shape having a leadingedge fore of the mast, and a trailing edge aft of the mast; the spreaderassembly including a fixed spreader unit secured to the flexible sailpanels defining the bottom of the flexible wing-sail and fixing it tothe bottom of the mast, and a plurality of slidable spreader unitssecured to the flexible sail panels at longitudinally spaced locationsthereof and slidable along the mast to permit hoisting and reefing theflexible wing-sail by unfolding and folding the wing-sail; each of thespreader units being configured, dimensioned and secured to the flexiblesail panels such as to permit flexibility between the leading andtrailing edges of the portion of the wing sail occupied by therespective spreader unit.

According to further features in the described preferred embodiment, thetrailing edge of each of the first and second sail panels is slidablycoupled to the boom by a slide movable within a slot in the boom andurged by a spring or by an elastic line outwardly of the boom away fromthe pivotal coupling of the boom to the mast.

According to another aspect of the present invention, there is provideda flexible wing-sail for wind-propelled vehicle, comprising: a mast tobe rotatably mounted in a vertical position on the vehicle; a pluralityof flexible sail panels carried by the mast; and a spreader assemblysecuring the flexible sail panels to the mast and imparting to theflexible sail panels an airfoil shape having a leading edge fore of themast, and a trailing edge aft of the mast; the spreader assemblyincluding a fixed spreader unit secured to the flexible sail panelsdefining the bottom of the flexible wing-sail and fixing it to thebottom of the mast, and a plurality of slidable spreader units securedto the flexible sail panels at longitudinally spaced locations thereofand slidable along the mast to permit hoisting and reefing the flexiblewing-sail.

According to further features in the described preferred embodiment, thefixed spreader unit is secured only to the sail panels at the leadingedge of the flexible wing-sail and fixes them to the bottom of the mast,and the slidable spreader units are secured only to the sail panels atthe leading edge of the flexible wing-sail and slidable mount them tothe mast.

According to yet another aspect of the present invention, there isprovided a flexible wing-sail for wind-propelled vehicles, comprising: amast to be rotatably mounted in a vertical position on the vehicle; aplurality of flexible sail panels carried by the mast; and a spreaderassembly securing the flexible sail panels to the mast and imparting tothe flexible sail panels an airfoil shape having a leading edge fore ofthe mast, and a trailing edge aft of the mast; the flexible sail panelsbeing secured to the spreader assembly by battens received in pockets inthe flexible sail panels;

each of said spreader units being configured, dimensioned and secured tothe flexible sail panels such as to permit flexibility between theleading and trailing edges of the portion of the wing sail occupied bythe respective spreader unit.

As will be described more particularly below, such a constructionpermits the flexible wing-sail to be hoisted, reefed, lowered, orotherwise adjusted in accordance with the apparent wind direction andwind velocity. The higher efficiency capability of such a flexiblewing-sail enables the vehicle to attain higher speeds of travel, oralternatively, to reduce the size of the sails and rigging. It enablesmore convenient operation of a vehicle driven by wind, and also enablessailing the vehicle more closely against the wind. In addition, itenables such advantages to be attained by a flexible wing-sail of arelatively simple construction.

Further features and advantages of the invention will be apparent fromthe description below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings, wherein:

FIG. 1 illustrates one form of water vehicle equipped with a flexiblewing-sail in accordance with the present invention;

FIG. 2 is a fragmentary view illustrating the rotary mounting of themast in the vehicle of FIG. 1;

FIG. 3 a is a fragmentary view illustrating the slidable mounting of thespreader units to the mast in the vehicle of FIG. 1;

FIG. 3 b is an enlarged fragmentary view of a portion of FIG. 3 a;

FIG. 4 is a horizontal sectional view of the flexible wing-sail in thevehicle of FIG. 1 to illustrate the structure of the slidable spreaderunits;

FIG. 5 is a top view illustrating the top spreader unit in the flexiblewing-sail of FIG. 1;

FIG. 6 is a fragmentary view of the upper end of the flexible wing-sailin FIG. 1;

FIG. 7 is a side elevational view of the flexible wing-sail in FIG. 1;

FIG. 8 is a top view illustrating another construction of slidablespreader unit that may be used in the flexible wing-sail;

FIG. 9 is a view similar to that of FIG. 8, but illustrating a stillfurther construction of slidable spreader unit that may be used;

FIG. 10 a is a top view illustrating a modification in the constructionof the top spreader unit that may be used;

FIG. 10 b is a fragmentary view illustrating the upper end of theflexible wing-sail when using the top spreader unit shown in FIG. 10 a;

FIGS. 11 a and 11 b illustrate the manner in which asymmetricalcurvatures to either port or starboard may be applied to the flexiblewing-sail of FIG. 1;

FIGS. 12 a, 12 b and 12 c diagrammatically illustrate the manner inwhich the curvature of the airfoil may be changed according to theapparent wind direction and force;

FIG. 13 diagrammatically illustrates a flexible wing-sail constructed inaccordance with the present invention equipped with motor drives formanually or automatically controlling the orientation and/or curvatureof the airfoil according to apparent wind conditions; and

FIG. 14 is a block diagram illustrating a control system which may beused for controlling the flexible wing-sail of FIG. 13 according to theapparent wind conditions.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1. illustrates a water vehicle including a hull 2 having avertically-extending mast 3 supporting a flexible wing-sail 4constructed in accordance with the invention. The mast 3 mounts theleading edge 4 a of the flexible wing-sail 4, whereas the trailing endof the flexible wing-sail is coupled to a boom 5 which is pivotallymounted at 6 to the mast 3. As will be described more particularlybelow, the flexible wing-sail 4 is made of a plurality of flexible sailpanels carried by the mast 3, and includes a spreader assembly spreadingthe flexible sail panels and securing them to the mast. The spreaderassembly imparts to the flexible sail panels an airfoil shape havingleading edge 4 a fore of the mast, and a trailing edge 4 b aft of themast.

The flexible wing-sail may be hoisted or lowered by a pair of halyards 7coupled to the upper end of the flexible wing-sail. The bottom end ofthe flexible wing-sail 4 is attached to the bottom part of the spreaderassembly, which in turn is rigidly attached to the mast 3. A bottom spar8 braces the leading edge of the flexible wing-sail 4, and anotherbottom spar 9 braces the boom 5.

The mast 3 is rotatably mounted to the hull 2. Thus, as shown in FIG. 2,the mast 3 is rotatably mounted between a rotary bearing 10 carried bythe bottom 11 of the hull 2, and by a second rotary bearing 12 carriedby the deck 13 of the hull.

As distinguished from conventional constructions, in this case therotary mast 3 may be selectively locked against rotation by means of abrake or other locking device. FIG. 2 illustrates one example of such alocking device including a disc 14 secured to the mast 3 and having anouter edge received within the locking device 15 secured to the vehicledeck 13. The locking device 15 shown in FIG. 2 includes a pair ofpressure plates 15 a, 15 b selectively actuated by an actuator 16 tofirmly engage the disc 14 in order to lock the mast 3 against rotation,or to disengage the disc in order to permit the mast to freely rotate.Actuator 16 may be hydraulically or pneumatically actuated via a controlline 17. It will be appreciated that other types of locking devices maybe used.

The flexible wing-sail 4 carried by the mast 3 is constructed of aplurality of flexible sail panels, as will be described moreparticularly below with respect to FIGS. 4 and 5. The sail panels attheir leading ends are spread apart by a spreader assembly including aplurality of vertically-spaced spreader units, one of which is shown at20 in FIGS. 3 and 4. As shown particularly in FIG. 4, battens 21,received in pockets in the flexible wing-sail 4, are secured to theouter ends of each spreader unit 20. Each spreader unit 20 furtherincludes a slide 22 slidable along rails 23 fixed to the opposite sidesof the mast 3.

It will thus be seen that, by appropriately manipulating the halyard 7(FIG. 1), the slidable couplings between the spreader units 20 and therails 23 of the mast 3, permit the flexible wing-sail 4 to be deployedto a fully hoisted position, as shown in FIG. 1, to a fully reefedposition, or to any partially reefed position in between.

FIGS. 4-7 illustrate the construction of the flexible wing-sail 4. It ismade of flexible sail panels each of sailcloth formed with pockets forreceiving the battens 21 which support and shape the flexible wing-sail.

Thus, as shown in FIG. 5, flexible wing-sail 4 is constructed of threeflexible sail panels, shown in broken lines at 26, 27 and 28 each formedwith the pockets for the battens 21. Flexible panel 26 extends on oneside to the trailing edge 4 b of the flexible wing-sail 4; flexiblepanel 27 extends on the opposite side to the trailing edge of theflexible wing-sail; and flexible panel 28 joins the leading ends of thetwo flexible panels 26, 27 to define the leading edge 4 a of theflexible wing-sail 4.

Flexible panels 26, 27, 28 may be constituted of a single sheet.Alternatively, they may be made of three separate panels sewn togetherat their respective edges and attached to the spreader units 20 byattaching their battens 21 to the ends of the spreader units.

Preferably, the battens 21 in sail panel 28 defining the leading edge 4a of the flexible wing-sail 4 are stiffer than the battens 21 in the twosail panels 26, 27 defining the sides of the flexible wing-sail. As willbe described more particularly below, the rounded configuration of theleading edge 4 a of the flexible wing-sail remains substantially thesame under all wind conditions, whereas the sail panels defining the twosides of the flexible wing-sail to the trailing edge 4 b of the flexiblewing-sail do change in curvature according to the apparent windconditions. For example, the battens 21 within the leading edge sailpanel 28 may be steel or plastic rods, whereas the battens in the sailpanels 26 and 27 may be fiber strands.

FIG. 5 illustrates one option wherein the top spreader unit 20 at theupper end of the flexible wing-sail 4 includes a transversely-extendingsection 20 a which, together with an axially-extending section 20 b,produces a thick, rounded, leading edge 4 a to the flexible wing-sail.The effective thickness of the airfoil decreases from the transversespreader unit 20 towards the trailing edge 4 b of the airfoil as shownparticularly in FIGS. 11 a and 11 b. As also shown in FIGS. 11 a and 11b, the bottom of the trailing edge of sail panel 26 terminates in aslide 31 received within a slot 31 a in the boom 5; and the bottom ofthe trailing edge of sail panel 27 terminates in a slide 32 receivedwithin a slot 32 a in the boom. Slide 31 of sail panel 26 is urgedoutwardly of the boom 5, that is, away from its pivotal mounting 6 tothe mast, by an elastic line or a spring member 34; and similarly, slide32 of sail panel 27 is urged outwardly of the boom by an elastic line ora spring member 35. As will be described below particularly with respectto the description of FIGS. 11 a, 11 b and FIGS. 12 a-12 c, such aconstruction permits the asymmetric shape of the airfoil to be changed,as desired, according to apparent wind conditions.

FIG. 6 illustrates the manner of hoisting and reefing the flexiblewing-sail illustrated in FIG. 5. Thus, one end of the halyards 7 wouldbe secured at points 20 c to the opposite ends of the axial section 20 bof the topmost spreader unit 20. The opposite ends of the halyards 7 arethen passed around rollers 42 carried by a top plate 33 at the upper endof the mast 3. The latter ends are grasped by the user such that pullingthe halyards hoists the flexible wing-sail, whereas releasing thehalyards permits the flexible wing-sail to be reefed by gravity.

FIG. 8 illustrates a flexible wing-sail of a similar construction asdescribed above, except that the spreader unit, therein designated 20′,is of a slightly different configuration than spreader unit 20 shown inFIGS. 4 and 5. Each spreader unit 20′ in FIG. 8 is also of a one partconstruction, being slidably mounted at its center on the mast 3′; italso, extends transversely of the leading edge of the flexible wing-sail4′, joining the leading edges of the two flexible panels 26′, 27′, tothe rounded panel 28′ at the leading edge of the flexible wing-sail.

FIG. 9 illustrates a slightly different construction wherein each of thespreader units is made of two sections, shown at 20 a″, 20 b″,respectively. One end of each section joins the rounded sail panel 28″at the leading edge of the flexible wing-sail to the respective sailpanels 26″, 27″. The opposite end of each section is slidably mounted tothe mast 3″. In all other respects, the flexible wing-sail illustratedin FIG. 9 is constructed and is used in the same manner as describedabove.

FIGS. 10 a and 10 b illustrate the option of mounting the halyards 7directly to the upper end of the flexible wing-sail to fully hoist it,to fully reef it, or to partially reef it. Thus one end of each halyard7 is coupled to a tab 41 secured to the top of the respective sail paneland passes around a roller 42 fixed to the top plate 33 at the upper endof the mast 3, such that the halyard may be pulled to hoist the flexiblewing-sail, or released to partially or fully reef it. As shown in FIG.1, the trailing end of the flexible wing-sail may be provided with aplurality of tabs 41 along its height, to enable the flexible wing-sailto be secured in a partially reefed condition.

FIGS. 11 a, 11 b illustrate the manner in which the flexible wing-sail 4may be formed into a desired asymmetric airfoil shape according to theapparent wind direction. For this purpose the aft end of the boom 5 isprovided with a boom line 40 which may be pulled towards the hull axis,in order to pivot the boom 5 with respect to the mast 3, when theflexible wing-sail direction is parallel to the wind and the mast islocked in place by the locking device 15 (FIG. 2). Thus, as shown inFIGS. 11 a and 11 b, when the mast is locked against rotation, pullingboom line 40 to pivot the boom 5 towards the hull axis will cause slides31 and 32, at the trailing edges of the two sail panels 26, 27, to slidewithin their respective slots 31 a, 32 a of the boom, thereby enablingthe curvature of the two sail panels 26, 27 to be increased; whereasreleasing the boom line to permit the boom to pivot away from the hullaxis by the wind force, will cause the slides 31, 32 to move in theirrespective slots, thereby decreasing the curvature of the sail panels upto a symmetrical airfoil configuration.

The battens 21 are preferably of varying thickness, being thicker at thefront end of the sail panels 26, 27, than at the trailing end 4 b. Eachbatten is attached at its front to the respective spreader unit 20, andat its rear to the respective sail panel 26, 27. Thus, when the wind isin the direction shown in FIG. 11 a and 11 b and the flexible wing-saildirection is parallel to the wind, pivoting the boom 5 towards the hullaxis causes, in both cases, the sail panel on the leeward side to assumea convex form, and the sail panel on the windward side to assume aconcave form. In this way, the airfoil shape of the flexible wing-sailassumes an asymmetric form in accordance with the wind direction,whether the wind is from the port or from the starboard side.

FIGS. 12 a-12 c illustrate the deployment of the flexible wing-sail 4under varying wind conditions.

In FIG. 12 a, the wind is of high velocity producing a high wind forceapplied to the flexible wing-sail. In this case, the mast lock 15 (FIG.2) would be released so that the mast 3 would freely rotate to enablethe flexible wing-sail to assume the direction of the wind, as shown inFIG. 12 a. In this case, the axis of the boom 5 is perpendicular to theaxis of the mast 3, so that the flexible wing-sail 4 assumes asymmetrical airfoil shape.

It will be appreciated that, in a high wind condition, the sail may bepartially reefed or fully reefed in order to decrease the wind forceapplied to the flexible wing-sail, although actually, the drag of theairfoil produced by a hoisted wing-sail is less than the drag producedby the mast itself in a fully reefed wing-sail.

FIG. 12 b illustrates the condition wherein there is a medium windforce. In this case, the mast 3, after assuming the wind direction,would be locked against rotation, and the boom line 40 would be pulledto pivot the boom 5 towards the hull axis. This will cause the airfoilto become asymmetric in shape and the angle of attack to increase, asdescribed above with respect to FIGS. 11 a and 11 b and as shown in FIG.12 b, which thereby increases the aerodynamic forces applied by the windto the flexible wing-sail.

FIG. 12 c illustrates the condition wherein there is very low windvelocity. In this case, the boom 5 is pivoted to a greater extenttowards the axis of the hull while the mast is locked against rotation.This increases the curvature of the airfoil as well as the angle ofattack, and thereby increases the aerodynamic forces applied by the windto the flexible wing-sail.

The flexible wing-sail as described above may be controlled as alreadydescribed without recourse to any mechanically drives. When such aflexible wing-sail is to be implemented in a larger vessel, and/or whenautomation is desired, the system may include electric or hydraulicmotors to control the various operations described above.

FIG. 13 diagrammatically illustrates a motorized control that may beused for the various control operations; and FIG. 14 diagrammaticallyillustrates a control system which may be used for either manual controlor automatic control.

Thus, as shown in FIG. 13, the mast 3 carrying the flexible wing-sail 4may be rotated by a motor M₁ via a gear 106 driven by the motor andmeshing with a gear 107 fixed to the mast. As also shown in FIG. 13, theboom 5 may be pivoted towards or away from the hull axis by a secondmotor M₂ driving a nut 108 with respect to a screw 109 coupled to theboom.

The vehicle may also include a third motor M₃ (FIG. 14) coupled to thehalyards (e.g., 7, FIG. 1) for raising and lowering the flexiblewing-sail.

FIG. 14 illustrates a control system, generally designated 110, whichmay be operated according to either a manual mode or an automatic mode,as may be selected by a mode selector 111. When the manual mode isselected, the rotary position of the mast may be controlled by manualcontrol device 112 which controls motor M₁ to rotate the mast; and thedegree of curvature of the airfoil may be selected by manual controldevice 113 which controls motor M₂ to pivot the boom. The deployment ofthe flexible wing-sail may also be controlled by a manual control device114 which controls motor M₃ to hoist or reef the flexible wing-sail.

On the other hand, when the automatic control is selected by the modeselector 111, motor M₁ which rotates the mast is automaticallycontrolled by a wind direction sensor 115 to maintain the flexiblewing-sail direction parallel to the apparent wind; and motor M₂ isautomatically controlled in response to a wind velocity sensor 116 tochange the angle of the boom with respect to the mast, and thereby theasymmetric curvature of the airfoil, in order to maintain the optimumairfoil shape in accordance with the apparent wind force.

It will thus be seen that when mode selector 111 of the controller 110selects the automatic mode, the flexible wing-sail automatically turnsinto the right direction relative to the apparent wind, and at the sametime, the airfoil shape is automatically adjusted to the right directionand the right degree of curvature so as to produce optimum aerodynamicefficiency.

A wind-driven vehicle constructed in accordance with the foregoingfeatures of the invention thus provides the skipper with full control oneverything required from a wing-sail. The effective surface area of theflexible wing-sail may be controlled by means of the halyards 7 topermit reefing as in a conventional sail; the direction of the flexiblewing-sail may be controlled by releasing the mast brake device 15,letting the flexible wing-sail to spontaneously rotate and assumedirection with respect to the apparent wind, and relock the mast brakedevice 15. In order to adjust the flexible wing-sail to the apparentwind force, the degree of asymmetry of the airfoil shape may becontrolled by changing the angle between the boom 5 and the mast 3. Thevehicle may include simple controls as described above, or the controlsmay be automated by a control system as also described above.

While the invention has been described above with respect to wind-drivenwater vehicles, it will be appreciated that the invention could also beimplemented in wind-driven land vehicles or ice vehicles. Many othervariations, modifications and applications of the invention will beapparent.

1. A flexible wing-sail for wind-propelled vehicles, comprising: a mastto be rotatably mounted in a vertical position on the vehicle enablingthe flexible wing-sail to freely rotate and assume parallel direction tothe apparent wind; a plurality of flexible sail panels carried by saidmast and including first, second and third sail panels defining theopposite sides and the trailing edge of the flexible wing-sail, and athird sail panel defining the leading edge of the flexible wing-sail; aspreader assembly securing said sail panels to the mast and imparting tothe sail panels an airfoil shape having a leading edge fore of the mast,and a trailing edge aft of the mast; a boom pivotally coupled above deckto the bottom of said mast and including a slidable coupling to thetrailing edge of each of said first and second sail panels; and a brakefor selectively locking the mast against rotation with respect to thevehicle, such that pivoting the boom while the mast is locked againstrotation, changes the curvature of the airfoil shape defined by thefirst and second sail panels according to the apparent wind directionand velocity.
 2. The flexible wing-sail according to claim 1, whereinthe trailing edge of each of said first and second sail panels isslidably coupled to said boom by a slide normally urged by an elasticelement rearwardly of the boom away from the pivotal coupling of theboom to the mast.
 3. The flexible wing-sail according to claim 1,wherein said spreader assembly includes a fixed spreader unit secured tothe flexible sail panels defining the bottom of the flexible wing-sailand fixing it to the bottom of the mast, and a plurality of slidablespreader units secured to the flexible sail panels at longitudinallyspaced locations thereof and slidable along said mast to permit hoistingand reefing the flexible wing-sail.
 4. The flexible wing-sail accordingto claim 3, wherein said fixed spreader unit is secured only to the sailpanels at the leading edge of the flexible wing-sail and fixes themabove deck to the bottom of the mast, and said slidable spreader unitsare secured only to the sail panels at the leading edge of the flexiblewing-sail and slidable mount them to the mast.
 5. The flexible wing-sailaccording to claim 1, wherein said first, second and third sail panelsinclude battens received in pockets in the respective sail panel, andwherein said spreader units are secured to said battens at the joinededges of the sail panels.
 6. A flexible wing-sail for wind-propelledvehicles, comprising: a mast to be rotatably mounted in a verticalposition on the vehicle; a plurality of continuous flexible sail panelscarried by said mast; and a spreader assembly securing said flexiblesail panels to the mast and imparting to the flexible sail panels anairfoil shape having a leading edge fore of the mast, and a trailingedge aft of the mast; said spreader assembly including a fixed spreaderunit secured to the flexible sail panels defining the bottom of theflexible wing-sail and fixing it to the bottom of the mast, and aplurality of slidable spreader units secured to the flexible sail panelsat longitudinally spaced locations thereof and slidable along said mastto permit hoisting and reefing the flexible wing-sail by unfolding andfolding the wing-sail; each of said spreader units being configured,dimensioned and secured to the flexible sail panels such as to permitflexibility between the leading and trailing edges of the portion of thewing sail occupied by the respective spreader unit.
 7. The flexiblewing-sail according to claim 6, wherein said fixed spreader unit issecured only to the sail panels at the leading edge of the flexiblewing-sail and fixes them to the bottom of the mast, and said slidablespreader units are secured only to the sail panels at the leading edgeof the flexible wing-sail and slidable mount them to the mast.
 8. Theflexible wing-sail according to claim 7, wherein said plurality of sailpanels include first and second sail panels defining the opposite sidesand the trailing edge of the flexible wing-sail, and a third sail paneldefining the leading edge of the flexible wing-sail.
 9. The flexiblewing-sail according to claim 8, wherein the flexible wing-sail furtherincludes a boom pivotally coupled to the bottom of said mast, thetrailing edge of each of said first and second sail panels beingslidably coupled to said boom.
 10. The flexible wing-sail according toclaim 9, wherein the mast includes a brake for selectively locking themast against rotation with respect to the vehicle, such that pivotingthe boom while the mast is locked against rotation, changes thecurvature of the airfoil shape defined by the first and second sailpanels.
 11. The flexible wing-sail according to claim 10, wherein thetrailing edge of each of said first and second sail panels is slidablycoupled to said boom by a slide normally urged rearwardly of the boomaway from the pivotal coupling of the boom to the mast.
 12. The flexiblewing-sail according to claim 11, wherein said slide is movable within aslot in said boom and is urged by a spring or by an elastic linerearwardly of the boom away from the pivotal coupling of the boom to themast.
 13. The flexible wing-sail according to claim 8, wherein saidfirst, second and third sail panels include battens received in pocketsin the respective sail panel, and wherein said spreader units aresecured to said battens at the joined edges of the sail panels.
 14. Theflexible wing-sail according to claim 13, wherein said battens in thepockets of the third sail panel are stiffer than those in the pockets ofsaid first and second sail panels.
 15. The flexible wing-sail accordingto claim 8, wherein each of said slidable spreader units is slidablymounted at its center to said mast, and is secured at one end to theedge of the first sail panel joined to the third sail panel, and at itsopposite end to the edge of the second sail panel joined to the thirdsail panel.
 16. The flexible wing-sail according to claim 8, whereineach of said slidable spreader units includes a first section slidablymounted at one end to said mast and at its opposite end to the edge ofthe first sail panel joined to the third sail panel, and a secondsection slidably mounted at one end to said mast and at the opposite endto the edge of the second sail panel joined to the third sail panel. 17.A wind-propelled vehicle including a flexible wing-sail according toclaim 1 and further including: an apparent wind direction and wind forcesensor; a motor for selectively rotating said mast; and a control systemhaving: (a) a manual mode of operation, wherein said motor is manuallycontrolled to change the direction of the flexible wing-sail withrespect to the apparent wind direction, and (b) an automatic mode ofoperation, wherein said motor is automatically controlled in response tothe apparent wind direction, as sensed by said wind direction sensor, tomaintain the flexible wing-sail direction parallel to the apparent winddirection.
 18. The wind-propelled vehicle according to claim 17, whereinsaid vehicle further includes a wind velocity sensor for sensing theapparent wind velocity, and a second motor for selectively pivoting theboom to different angles with respect to the mast; and wherein, in saidcontrol system, the manual mode of operation also permits manual controlof said second motor to change the angle of the boom with respect tosaid mast, and thereby to change the curvature of the airfoil shape; andsaid automatic mode of operation automatically controls said secondmotor to change the angle of the boom with respect to the mast, andthereby the curvature of the airfoil shape, in response to the apparentwind velocity as measured by said wind velocity sensor.
 19. A flexiblewing-sail for wind-propelled vehicles, comprising: a mast to berotatably mounted in a vertical position on the vehicle; a plurality offlexible sail panels carried by said mast; and a spreader assemblysecuring said flexible sail panels to the mast and imparting to theflexible sail panels an airfoil shape having a leading edge fore of themast, and a trailing edge aft of the mast; said flexible sail panelsbeing secured to said spreader assembly by battens received in pocketsin said flexible sail panels; each of said spreader units beingconfigured, dimensioned and secured to the flexible sail panels such asto permit flexibility between the leading and trailing edges of theportion of the wing sail occupied by the respective spreader unit. 20.The flexible wing-sail according to claim 19, wherein said spreaderassembly includes a fixed spreader unit secured to the flexible sailpanels defining the bottom of the flexible wing-sail and fixing it tothe bottom of the mast, and a plurality of slidable spreader unitssecured to the flexible sail panels at longitudinally spaced locationsthereof and slidable along said mast to permit hoisting and reefing theflexible wing-sail.
 21. The flexible wing-sail according to claim 19,further comprising: a boom pivotally coupled at one end to the bottom ofsaid mast and slidably coupled at the opposite end to the trailing edgeof said sail panels by slides normally urged rearwardly of the boom byelastic elements; and a brake for selectively locking the mast againstrotation with respect to the vehicle, such that pivoting the boom whilethe mast is locked against rotation, changes the curvature of theairfoil shape according to the apparent wind direction and velocity.